Belt tensioning device



Dec. 22, 1959 D. E. WILLIAMSON 2,917,986

BELT TENSIONING DEVICE Fild May 11, 1955 BELT TENSIONING DEVICE A UnitedStates Patent Donald E. Williamson, West Concord, Mass., assignor,

by mesne assignments, to Kalvar Corporation, New Orleans, La., acorporation of Louisiana Application May 11, 1955, Serial No. 507,634

1 Claim. eras-47.5

It is desirable for various purposes to utilize a nip between adrum-like structure and belt means fastened thereto and alternatelywinding on and unwinding from the drum, as the latter is reciprocated.In order to maintain firm contact between the drum and the belt at thenip, the belt must be tightly pulled around the drum periphery,regardless of, the position of the drum. This situation is for exampleencountered in apparatus for W photographic contact printing where twosheets-an original tobe reproduced and the photographic stockhave to bebrought into close contact in a nip of the above mentioned type whichpermits easy charge and discharge of the sheets and confinement thereoffor exposure during a predetermined period of time. i

Some of the objects of the invention are to provide a devicefortightening a belt means around a rotating drum means to which one end ofthe belt means is light sensitive sheets into a nip between a drum and aweb for retaining it therein during a predetermined period of time andfor removing it therefrom by a reverse movement; and to provide such adevice which is suited for the mounting of an elongate light sourcewithin the drum. While the device according to the invention isespecially suited for photographic purposes, it is useful whereversimilar problems are present.

A summary indicating the nature and substance of the invention is asfollows.

According to the invention, a device for tensioning a belt means woundon and fastened at one end to a rotatable drum means comprises a beltreceiving roller rotatably mounted parallel to the drum means and havingfastened thereto the other end'of the belt means; a compensation rollerrotatably mounted coaxially with the receiving roller; resilient meansinterposed between the two rollers for exerting an essentially constanttorque; and rope or cable-like means wound about the drum means and thecompensation roller in a sense opposite to that in which the belt meansis wound thereon; whereby the resilient means maintains through the ropemeans a constant tension on the belt means, the tensions on the ropemeans and on the belt means opposing each other for all positions of thedrum.

In a particularly'practical aspect of the invention, the resilient meansis a helical spring arranged about a pivot that coaxially connects thetwo rollers, and one end of which spring is fastened to the receivingroller whereas its other end is fastened to the compensation roller.

The following description of a typical embodiment illustrates these andother objects, and aspects of the 'unessential with regard to 2,917,986Patented Dec. 22, 1959 nature of the invention. This description refersto a drawing in which:

' Fig. l is an axonometric view of a device according to the invention;

Fig. 2 is a schematic side elevation taken from the right-hand side ofFig. 1; and

Fig. 3 is an axial section through the end portion of the web receivingroller and the compensation roller, this part being indicated at T ofFig. 1.

Figs. 1 and 2 indicateat 11 an essentially linear source of light suchas a high intensity gas discharge lamp of known design, supplied fromterminals on either side of the tubular lamp envelope, one of whichterminals is indicated at 11.1. The structural details of the lamp arenot shown because they are not essential with respect to the presentinvention. The lamp 11 is surrounded by a translucent cylindrical drum12 made of suitably strong material, such as Lucite. The drumis'rotatably mounted on a frame by suitable means such as flange andsupporting rolls on eachside, as indicated at 14 and 15 of Fig. 2. Theconstruction of these pivotsis the invention and therefore not describedin detail. i I

Mounted rotatablyon an axis a by conventionalmeans is arranged a"beltreceiving roller 21' with pivot shaft 21.1 and, coaxial therewith, aspring barrel 22 which constitutes the compensation roller and isassociated with thebelt receiving roller 21 as shown at T in Fig. 3. Thebarrel 22 rotates on a shaft 25 which has a portion 25.1

of reduced diameter which portion is fastened in a bore 21.2 of theroller 21. A spring 31 is inserted in the annular space 32 ofbarrel 22,and one end 31.1 of the spring is fastened to the barrel 22 whereas theother end 31.2 of the spring is fastened to the face of roll 21.

In this manner the roller-21 and the barrel 22 can rotate relatively toeach other 'on' 25.5 and 25.6 while both rolls rotate also on 21.1 and25, respectively. Suitable lubrication being provided, the two rollerscan rotate relatively to each other.

A belt means, such as a web 41 is fastened to a groove of the drum 12for example by means of a strip 42 and screws 43. The web is woundaround drum 12 for example to the extent indicated in Fig. 2, and woundin opposite direction around the receiving roller 21. In this positionthe larger portion is on the drum. When the web is unwound from thedrum, it is received on the roller 21 which will then carry severalturns of the web. The web is suitably fastened to the roller 21, forexample in the manner in which it is fastened to the drum 12.

A cable or rope 71 is wound around the drum 12 in a direction oppositeto that of web 41. The cable can be contained in an annular recess ofthe drum, which is not shown for the sake of simplicity. The cable 71 isalso wound around the barrel 22 in opposite direction to the web 41 andit is suitably fastened to the drum and the roller as indicated at 41.1and 41.2 of Figs. 1 and 2. The barrel 22 can be provided with a flange22.1 in order to retain the rope in proper position. The free side ofthe roller 21 has suitable pivot means as indicated at 21.1 of Fig. 1,and bearings (not shown) are provided at 21.1 and 25. The device can bedriven in various ways; the present embodiment is driven by way of acoupling indicated at 25.2. Reciprocating movement is provided by meansof a suitable reversible drive connected to clutch 25.2.

The above described embodiment is intended for purposes of makingphotographic copies, where an original and a sheet of photographic paperare fed, with the assistance of the platform provided by the web, intothe nip between drum and web, with the latter in the position gara esindicated in Fig. 2 by the position 42.1 of the web fastening strip 42,and the platform indicated at 41. The drum and the roller are thenrotated into the position shown in Figs. 1 and 2 by strip 42, asindicated by arrow b, and are now ready for exposure by. lamp 11. Afterexposure, the drum and the roller are rotated in the direction of arrow0, by reversing the drive which is coupled to the device at 25.2. Itwill be noted that, with the drum end of the web in position 42.1,practically the entire web has been received on roller 21.

In order to keep the original and the photographic paper in closecontact when they are confined, for exposure to lamp 11, in the nipbetween the drum and the web, the latter must be drawn tightly aroundthe drum, with constant tension; this tension is securely provided bythe device T as follows:

The torsional tension of the spring 31 is so adjusted that it exerts aforce between the cable 71 which is wrapped around the drum and thereceiving roll in the opposite direction from that of the web 41. Itwill be evident that the web 41 will always be tightly wound in allpositions of the cylinder, if an initial rotary tension is applied tothe spring 31, for example upon fastening the rope at 41.2 to thereceiving roller.

, It should be understood that the present disclosure is for the purposeof illustration only and that this 'invention includes all modificationand equivalents which fall within the scope of the appended claim.

I claim:

A device for the contact printing of photographic sheet material,comprising: a translucent drum rotatably mounted on a fixed essentiallyhorizonal axis; elongate lamp means within said drum; a belt wound onand fastened at one end to said drum; a belt receiving roller rotatablymounted parallel to said drum on a fixed axis, with its surfaceappreciably separated from the surface of the drum, and having fastenedthereto the other end of said belt which is wound thereon in a senseopposite to that on said drum so that the nip formed by said drum andsaid belt presents an open end towards the receiving roller such as toform a platform in substantially fixed position provided by the beltportion between the two surfaces; a compensation roller rotatablymounted coaxially with and adjacent to said receiving roller; a cablewound about said drum and said compensation roller in a sense oppositeto that in which said belt is wound on said drum and said receivingroller; torque means interposed between said rollers for tending torotate said rollers in opposite direction; and means for reciprocatingsaid drum and said rollers with said belt and said cable; whereby thetorque means maintains through the cable a constant tension on the webfor all positions of the drum, so that the photographic sheet materialcan be fed on the platform to the open end of the nip when the web isunwound from the drum, then brought into the nip for exposure by thelamp, by rotation of the drum and the rollers, and returned through saidopen end by reverse rotation, and wherein said compensation roller hasan annular recess facing said receiving roller; one of said rollers hasan axial bore and the other roller has an axial projection fitting saidbore; and the torque means includes a spring means helically woundwithin said' recess with one end fixed to em roller and with the otherend fixed to the other roller.

References Cited in the file of this patent UNITED STATES PATENTS789,773 Wagenhorst May 16, 1905 1,093,623 Herman Apr. 21, 1914 1,886,202Langsner Nov. 1, 1932 2,024,678 Brunk Dec. 17, 1935 2,383,785 FosterAug. 28, 1945 2,585,519 Van Der Grinten Feb. 12, 1952 2,653,529 StoverSept. 29, 1953 FOREIGN PATENTS 709,542 Great Britain May 26, 1954

